Modular Policy Framework lets you configure special actions for many application inspections. When you enable an inspection engine in the Layer 3/4 policy map, you can also optionally enable actions as defined in an inspection policy map. When the inspection policy map matches traffic within the Layer 3/4 class map for which you have defined an inspection action, then that subset of traffic will be acted upon as specified (for example, dropped or rate-limited).

Information About Inspection Policy Maps

An inspection policy map consists of one or more of the following elements. The exact options available for an inspection policy map depends on the application.

•Traffic matching command—You can define a traffic matching command directly in the inspection policy map to match application traffic to criteria specific to the application, such as a URL string, for which you then enable actions.

–Some traffic matchingcommands can specify regular expressions to match text inside a packet. Be sure to create and test the regular expressions before you configure the policy map, either singly or grouped together in a regular expression class map.

•Inspection class map—(Not available for all applications. See the CLI help for a list of supported applications.) An inspection class map includes traffic matching commands that match application traffic with criteria specific to the application, such as a URL string. You then identify the class map in the policy map and enable actions. The difference between creating a class map and defining the traffic match directly in the inspection policy map is that you can create more complex match criteria and you can reuse class maps.

–Some traffic matchingcommands can specify regular expressions to match text inside a packet. Be sure to create and test the regular expressions before you configure the policy map, either singly or grouped together in a regular expression class map.

•Parameters—Parameters affect the behavior of the inspection engine.

Guidelines and Limitations

•HTTP inspection policy maps—If you modify an in-use HTTP inspection policy map (policy-map type inspect http), you must remove and reapply the inspect httpmap action for the changes to take effect. For example, if you modify the "http-map" inspection policy map, you must remove and readd the inspect http http-map command from the layer 3/4 policy:

hostname(config)# policy-map test

hostname(config-pmap)# class http

hostname(config-pmap-c)# noinspect http http-map

hostname(config-pmap-c)# inspect http http-map

•All inspection policy maps—If you want to exchange an in-use inspection policy map for a different map name, you must remove the inspectprotocol map command, and readd it with the new map. For example:

hostname(config)# policy-map test

hostname(config-pmap)# class sip

hostname(config-pmap-c)# noinspect sip sip-map1

hostname(config-pmap-c)# inspect sip sip-map2

Default Inspection Policy Maps

The default inspection policy map configuration includes the following commands, which sets the maximum message length for DNS packets to be 512 bytes:

policy-map type inspect dns preset_dns_map

parameters

message-length maximum 512

Note There are other default inspection policy maps such as policy-map type inspect esmtp _default_esmtp_map. These default policy maps are created implicitly by the command inspectprotocol. For example, inspect esmtp implicitly uses the policy map "_default_esmtp_map." All the default policy maps can be shown by using the show running-config all policy-map command.

Defining Actions in an Inspection Policy Map

When you enable an inspection engine in the Layer 3/4 policy map, you can also optionally enable actions as defined in an inspection policy map.

Restrictions

You can specify multiple class or match commands in the policy map.

If a packet matches multiple different match or class commands, then the order in which the adaptive security appliance applies the actions is determined by internal adaptive security appliance rules, and not by the order they are added to the policy map. The internal rules are determined by the application type and the logical progression of parsing a packet, and are not user-configurable. For example for HTTP traffic, parsing a Request Method field precedes parsing the Header Host Length field; an action for the Request Method field occurs before the action for the Header Host Length field. For example, the following match commands can be entered in any order, but the match request method get command is matched first.

match request header host length gt 100

reset

match request method get

log

If an action drops a packet, then no further actions are performed in the inspection policy map. For example, if the first action is to reset the connection, then it will never match any further match or class commands. If the first action is to log the packet, then a second action, such as resetting the connection, can occur. (You can configure both the reset (or drop-connection, and so on.) and the log action for the same match or class command, in which case the packet is logged before it is reset for a given match.)

If a packet matches multiple match or class commands that are the same, then they are matched in the order they appear in the policy map. For example, for a packet with the header length of 1001, it will match the first command below, and be logged, and then will match the second command and be reset. If you reverse the order of the two match commands, then the packet will be dropped and the connection reset before it can match the second match command; it will never be logged.

match request header length gt 100

log

match request header length gt 1000

reset

A class map is determined to be the same type as another class map or match command based on the lowest priority match command in the class map (the priority is based on the internal rules). If a class map has the same type of lowest priority match command as another class map, then the class maps are matched according to the order they are added to the policy map. If the lowest priority command for each class map is different, then the class map with the higher priority match command is matched first. For example, the following three class maps contain two types of match commands: match request-cmd (higher priority) and match filename (lower priority). The ftp3 class map includes both commands, but it is ranked according to the lowest priority command, match filename. The ftp1 class map includes the highest priority command, so it is matched first, regardless of the order in the policy map. The ftp3 class map is ranked as being of the same priority as the ftp2 class map, which also contains the match filename command. They are matched according to the order in the policy map: ftp3 and then ftp2.

The policy_map_name argument is the name of the policy map up to 40 characters in length. All types of policy maps use the same name space, so you cannot reuse a name already used by another type of policy map. The CLI enters policy-map configuration mode.

Step 3 To apply actions to matching traffic, perform the following steps.

•Specify traffic directly in the policy map using one of the match commands described for each application in the applicable inspection chapter. If you use a match not command, then any traffic that matches the criterion in the match not command does not have the action applied.

b. Specify the action you want to perform on the matching traffic by entering the following command:

Identifying Traffic in an Inspection Class Map

This type of class map allows you to match criteria that is specific to an application. For example, for DNS traffic, you can match the domain name in a DNS query.

A class map groups multiple traffic matches (in a match-all class map), or lets you match any of a list of matches (in a match-any class map). The difference between creating a class map and defining the traffic match directly in the inspection policy map is that the class map lets you group multiple match commands, and you can reuse class maps. For the traffic that you identify in this class map, you can specify actions such as dropping, resetting, and/or logging the connection in the inspection policy map. If you want to perform different actions on different types of traffic, you should identify the traffic directly in the policy map.

Restrictions

Not all applications support inspection class maps. See the CLI help for class-map type inspect for a list of supported applications.

The class_map_name argumentis the name of the class map up to 40 characters in length.

The match-all keyword is the default, and specifies that traffic must match all criteria to match the class map.

The match-any keyword specifies that the traffic matches the class map if it matches at least one of the criteria.

The CLI enters class-map configuration mode, where you can enter one or more match commands.

Step 3 (Optional) To add a description to the class map, enter the following command:

hostname(config-cmap)# descriptionstring

Step 4 Define the traffic to include in the class by entering one or more match commands available for your application.

To specify traffic that should not match the class map, use the match not command. For example, if the match not command specifies the string "example.com," then any traffic that includes "example.com" does not match the class map.

To see the match commands available for each application, see the appropriate inspection chapter.

Examples

The following example creates an HTTP class map that must match all criteria: